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BASIC THEORY

CARBONATE RESERVOIR CHARACTERIZATION

STATIC AND DYNAMIC RESERVOIRCHARACTERIZATION

Static Properties :StratigraphyGeometry of reservoir and component faciesLithologyPorosity and permeabilityOther petrophysical propertiesStructure

TemperatureFluid compositions ?

Dynamic Properties :SaturationsPressureFluid contactsProduction and flow ratesRock/fluid impedances (and seismic amplitudes)Fluid compositions ?

Others ???

OVERVIEWTHE IMPORTANCE AND IMPLICAT IONS

OF RESERVOIR HETEROGENEITY

• The rationale for characterization of heterogeneous reservoirs is one offundamental economic

• Recent geological analyses indicate that most reservoirs display significantgeologic variation and compartementalization

• Reserve and distribution of mobile oil is very much a function of reservoirheterogeneity at meso- and macroscopic scales

• Designing a reliable reservoir model is a function of tectonic complexity , depositional environment , well spacing and the available cores and logs

• Reservoir heterogeneity in carbonate rocks is much complicated than insiliciclastic rocks due to its different origin and diagenetic process

HETEROGENEITY OF CARBONATE RESERVOIR

DEPOSITIONAL PROCESS

DIAGENESIS

PORE GEOMETRYSHAPE ; SIZE ; INTERCONNCTIVITY

CLASTICSCARBONATES

CARBONATESCLASTICS

POSITION INHYDROCARBON COLUMN

RESERVOIR QUALITYPOR ; PERM ; Sw ; So ; Rel.Perm; Po

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CHANGE PROPERTIES

DIAGENESIS and SECONDARY POROSITY

RESERVOIR QUALITY IN CARBONATE ROCKS

• IS A FUNCTION OF :- DEPOSITIONAL TEXTURES- ORIGINAL MINERALOGY- DIAGENESIS

• CAN BE PREDICTED THROUGH DEPOSITIONALFACIES ANALYSIS AND DIAGENETIC ANALYSIS( by applying sequence stratigraphy approach )

BASIC IDEA ……………………

POTENTIAL CARBONATE RESERVOIRS PASS THROUGH SEVERAL DIAGENETIC ENVIRONMENT

AFTER DEPOSITION

• EACH DIAGENETIC ENVIRONMENT LEAVES ANIMPRINT ON THE ROCK

• THE FINAL PORE NETWORK IS A RESULT OF THE DIAGENETIC PATHWAY EXPERIENCED BY THE RESERVOIR

• ALL CARBONATE DEPOSITIONAL TEXTURE MAY DEVELOPECONOMIC PORE NETWORKS THROUGH FAVORABLE DIAGENESIS

BASIC IDEA ……………………

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Dunham’s Classification of Limestone

REEFLIMESTONE

JAMES & BOURQUE,1992FLOATSTONE RUDSTONE

BAFFLESTONE BINDSTONE FRAMESTONE

CARBONATE FACIES BELTS

a. Mechanical breakdown ofHalimeda and Acropora

coral skeletonsb. Biological Breakdown of

massive corrals by sponges,fish , and urchins

( after Folk and Robles , 1964 )

PROCESS CONTROLLING DOMINANT GRAIN-SIZE FRACTIONS IN CARBONATE ROCKS :

PROCESS CONTROLLINGDOMINANT GRAIN-SIZE

FRACTIONSIN CARBONATE ROCKS :

a. Mechanical breakdown ofHalimeda and Acropora

coral skeletonsb. Biological Breakdown of

massive corrals by sponges,fish , and urchins

( after Folk and Robles , 1964 )

HYDRAULIC BEHAVIOUR OF GRAINS

- THRESHOLD VELOCITY- SETTLING VELOCITY- HJULSTROM’S DIAGRAM

Quartz

Problem mixed siliciclastic-carbonate sediments :Specific gravity of : Quartz – 2.65 Aragonite – 2.94

Calcite – 2.71

Bulk density + intraporousityCoral fragments e.g. Porites 1.2 (porous)

Agaricia 2.0 (compact)Mollusc + 2.0

Carbonate particle

Grains of similar size and shape will behave differently ina fluid due to their different bulk densities. Conversely ,grains of different shapes and sizes may be hydraulicallyequivalent.

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Cation Ionic Radii and Common Carbonate Minerals(after Speer, in Reeder (eds.) 1983)

Cation Ionic radius(nm) Minerals Crystal habit

Ni 0.069 Gaspeite NiCO3Mg 0.072 Magnesite MgCO3Zn 0.072 Smithsonite ZnCO3Co 0.075 Sphaerocobalite CoCO3 RhombohedralFe 0.078 Siderite FeCO3 (trigonal system)Mn 0.083 Rhodochrosite MnCO3Ca 0.100 Calcite CaC03

Ca 0.118 Aragonite CaCO3Sr 0.131 Strontianite SrCO3 OrthorhombicPb 0.135 Cerussite PbCO3Ba 0.147 Witherite BaCO3

CaCO3Three common polymorphs

1) Lo-Mg Calcite- most abundant sedimentary carbonate mineral- primary constituent of limestone- dissolves in acidic water- contains mol 1 – 4 mol % Mg

2) Hi-Mg Calcite- more soluble than calcite- contains 4 – 20+ mol % Mg- common in modern sediments, rare in limestone

3) Aragonite- highly soluble- same composition as Lo-Mg calcite, but with

different crystallinity- common in modern sediments, rare in limestone

Aragonite : Present-day coralsSome mollusks

Low-Mg calcite :Some mollusksSome foraminifera (including all deep-sea sp.)BrachiopodsUnicellular plant family(Coccolithophoridae deep-sea sediments & chalk)

High-Mg calcite :EchinodermsSome large foraminifera

DEPOSITION OF THE CARBONATE MINERALS DUE TO THE ACTION OF ORGANISMS

ORGANISMS AND MINERALOGYCalcareous Green Algae Aragonite

Sponges Mg-CalciteCoelenterates (Modern) AragoniteCoelenterates (Ancient ) Aragonite & CalciteBryozoans Calcite & Mg-CalciteBrachiopods CalciteMolluscs Aragonite & Calcite-

Mg-Calcite

Echinoderms Mg-Calcite

Calcareous Red Algae MgCalciteCoccolith CalciteForaminifera Calcite & Mg-Calcite

3. Aragonite grains either dissolve to form moldic pores or recrystallize to a coarser crystalline calcite that preserves grain texture but develops no porosity (Loucks and Brown, 1988).

1. Grains that are originallycalcite show little macroscopicevidence of alteration.

2. Mg-calcite grains commonlyconvert to calcite with no associate porosity developed.

In a few areas (e.g Jurassic and Lower Cretaceous of the Gulf Coast), Mg calcite grains have recrystallized to microrhombiccalcite, producing microporositybetween the rhombs.

In rare cases Mg-calcite dissolves Completely to yield moldic porosity.

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( Loucks and Brown , 1988 )

DIAGENETIC ENVIRONMENTS AND PRODUCT

SL1

MP

BZ

SL2

MTV

MTP

MP

BZ

SL3

MP

U

BZ

MP : Marine pure-atic zone

MTV : Meteoric va-doose zone

MTP : Meteoric pure-atic zone

BZ : Burial zoneU : UnconformitySL : Sea Level

DEVELOPMENT OF DIAGENESIS

INITIALLY POROUS& PERMEABLE

RQ poor RQ good RQ moderate RQ moderate RQ moderate - good

MARINE DIAGENESISCementation / No dissolution

EXPOSED

no yes

no

COMPACTIONLIMITED ?yes no

CLOSE TOUNCONFORMITY

yes

no

METEORIC PHREATICLimited dissolution

CementationPoro/Perm decrease

METEORIC VADOSE

yes

Extensive dissolutionLimited cementation

Porosity increase

DIAGENESIS

EFFECT OF DIAGANESIS ON RESERVOIR QUALITY HETEROGENEITY OF CARBONATE RESERVOIR

DEPOSITIONAL PROCESS

DIAGENESIS

PORE GEOMETRYSHAPE ; SIZE ; INTERCONNCTIVITY

CLASTICSCARBONATES

CARBONATESCLASTICS

POSITION INHYDROCARBON COLUMN

RESERVOIR QUALITYPOR ; PERM ; Sw ; So ; Rel.Perm; Po

( L k d B 1988

RELATIONSHIP BETWEEN FACIES, DIAGENESISAND POROSITY IN CARBONATE RESERVOIRS

PRIMARYPOROSITY

SECONDARYPOROSITY

1. INSIGNIFICANTDIAGENESIS

2. FABRIC SELECTIVEDIAGENESISEg. Biomoldic porosity

3. ENVIRONMENT RELATEDEg. ‘Beach rock’ cement

4. DATUM RELATEDEg. parallel to water tableor unconformityor petroleum /water contact

5. STRUCTURE RELATEDEg. fractures over salt domes,

dolomitization adjacent to faults

DECREASINGAPPLICATION

OFFACIES ANALYSIS

TO RESERVOIRPREDICTION

CARBONATE ROCKS TEXTURES AND COMMON POROSITY TYPES( Loucks and Brown , 1988 )

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CARTOON OF PORE GEOMETRIES IN CARBONATE ROCKS

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( After Esteban and Klappa , 1983 )

Examples of Characteristics of GR and Sonic Log of Paleokarst Development

IN MESOZOIC CARBONATES,OFFSHORE NORTHERN SPAIN

MODEL………………….

DIAGENETIC ENVIRONMENTSCARBONATE DIAGENETIC ENVIRONMENTS

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SIZE and SORTING

SILICICLASTIC

1. Provide a criterion for interpreting transportation, depositionand textural maturity

2. Relate to porosity, permeability and pore size3. After diagenesis : porosity and permeability ~ initial depositional

texture

CARBONATE

1. Depend on both hydraulic condition and organic productivity atthe site of deposition

2. Carbonate grains have a wide variety of size and shape difficult to relate size and sorting with porosity and permeability

3. Degree of diagenetic modification is more intensive lack of relatedevidence between observable texture and depositional texture